This application claims the priority benefit of Taiwan application serial no. 90103094, filed Feb. 13, 2001.
1. Field of the Invention
The present invention relates to a method for preventing corrosion of a furnace. More specifically, the present invention relates to a method for preventing corrosion of a furnace by a corrosive gas such as gaseous hydrogen chloride.
2. Description of the Related Art
When thermal oxidation is carried out in a conventional furnace, acidic side products, such as hydrogen chloride, are always generated when silicon dioxide is formed. Since the bottom of the furnace is made of metal iron, the acidic side products contact with the bottom of the furnace when the acidic side products exit from the furnace as a stream. The acidic side products react with the metal iron of the furnace bottom as follows:
2Fe+6HClxe2x86x922FeCl3+3H2
When iron is exposed in an acidic environment, especially one containing hydrogen chloride in a high temperature, FeCl3 is often generated on the surface of iron causing damage on the bottom. FeCl3 restricts the formation of a thermal oxide layer in a subsequent step and the formation of an oxide layer obtained by chemical vapor deposition.
Moreover, when the bottom of the metal is corroded, a new bottom is required to replace the corroded one. If corrosion occurs, the bottom has a shorter service life. Furthermore, not only the bottom is subject to corrosion, but also any part in the furnace made of metal can be corroded.
In one aspect of the present invention, an anti-corrosion furnace in which a dense be oxide alloy film is formed on the surface of the bottom tray to prevent corrosion of the bottom tray by an acidic substance is provided to overcome the problems in the prior art.
In another aspect of the present invention, a method for preventing corrosion of a furnace by a corrosive gas is provided. In the present invention, the material for the bottom tray of the furnace is made of an anti-corrosion alloy such as molybdenum and chromium. An oxygen-containing gas pipe is also provided in the furnace for charging the oxygen-containing gas. The oxygen-containing gas is reacted in a high temperature to form a purple oxide alloy film on the surface of the alloy tray.
The oxide alloy film of the present invention can prevent the reaction between acidic substances and the alloy tray, which would not adversely affect the quality of the oxide formed in a subsequent step.